I chrono’d some 22 ammunition in two guns today. Specifically, I wanted to understand why one gun likes CCI Standard Velocity but jams on Federal Gold Medal Match 711B, and the second gun does the opposite.
Here are the raw results:
|S&W 41||S&W 41||Ruger III||Ruger III|
|CCI SV||Fed 711B||CCI SV||Fed 711B|
First, the Smith & Wesson Model 41 likes CCI Standard Velocity as many owners know. This is the ammunition recommended by Smith & Wesson. And as you can see from the above data, when the Federal Gold Medal Match 711B ammunition is fired through that gun, the muzzle velocity averages about 50 ft/sec faster (958.7 CCI SV versus 1010.2 for Federal 711B).
And conversely, my Ruger Mk III prefers the Federal ammunition but jams on the CCI. Again, comparing the muzzle velocities in that gun, the CCI is about 35 ft/sec slower (902.1 versus 936.2). Ruger suggests using standard to higher velocity ammunition in this gun and my observed reliability versus the muzzle velocities seem to bear this out.
Note the final “S.D.” (Standard Deviation) row. It is generally thought that a lower Standard Deviation will result in less variation from shot to shot in terms of reliability of function.
This data suggests that, in each gun, the CCI Standard Velocity ammunition has less variation in muzzle velocity from shot to shot. But in the Ruger, that lower variability is obviated by the lesser reliability.
Another interesting effect is barrel length. The S&W has a seven inch (7″) barrel whereas the Ruger’s is five and a half inches (5.5″) long. That extra inch and a half appears to impart an additional 50 ft/sec to the CCI bullet, and even more with the Federal, another 75 ft/sec. (Ammunition manufacturers measure muzzle velocities in a 21″ rifle barrel hence their even greater published velocities.)
But does that extra 5% muzzle velocity help? Does the bullet fly straighter? Is it deflected less by the wind? Does the spinning bullet maintain its stable flight longer because of it?
This data also suggests that the pressure curve of the CCI ammunition is possibly sharper and an increase in barrel length imparts less additional velocity than the possibly slower powder — producing a broader pressure curve, perhaps — of the Federal ammunition where a longer barrel is able to use that extended pressure buildup.
Imagining an even longer barrel, we might even surmise that the burn rate and pressure curve in a short barrel might result in muzzle velocities that are challenging to infer from manufacturer’s measured velocities from 21″ barrels. Longer barrels do result in high muzzle velocities, this is true, but the data gathered here suggests that the Federal would continue to lengthen its lead in velocity over the CCI. And that in turn suggests that if there is a magic “feet per inch” velocity for a given gun, then the only way to find it is to try brands of ammunition that suggest they might fall in the appropriate range.
Ultimately of course, the real question is which ammunition is both reliable and accurate in each respective gun.
I have reliable ammunition for each gun and, from the measured differences in muzzle velocity and the effect that has on recoil and, therefore, the strength of the recoil spring in each of these two guns, I think I understand what’s happening.
And it’s probably true that the S&W Model 41 would shoot with similar reliability with just about any brand of ammunition with similar characteristics to CCI Standard Velocity. And for the Ruger, the extra oomph in the Federal Gold Medal Match 711B sets the mark when shopping for ammunition for that gun.
That’ll have to wait for another day.
Oh, one additional note.
I also tested some of the paper boxed CCI Standard Velocity and, lo and behold, it resulted in significantly different muzzle velocities from the plastic boxed CCI Standard Velocity (whose results appear above). In a nutshell, the paper boxed ammunition was an average of 60 ft/sec faster than that in the plastic box, and was therefore even “hotter” in the S&W 41 than the Federal Gold Medal Match 711B.
Although not tested, this suggests that the paper boxed CCI Standard Velocity ammunition might be a viable candidate for testing in the Ruger which prefers these higher velocities whereas the S&W 41 prefers the plastic boxed ammo.
So the next time the grocery clerk asks if you prefer paper or plastic, the answer just might be, “Ruger or Smith?”